Ion implantation offers great commercial promise for the improvement of the surface characteristics of a variety of materials, including metals, ceramics and plastics. In the conventional ion implantation process, ions are formed into a beam and accelerated to high energy before being directed into the surface of a solid target. thermodynamic constraints of more conventional techniques, ion implantation allows new materials to be produced with new surface properties. In particular, implantation can be used to improve greatly the friction, wear and corrosion resistance properties of the surfaces of metals. For example, implantation of nitrogen ions in a titanium alloy artificial hip joint has increased the joint lifetime by a factor of 400 or more. The properties of ceramic components and ceramic cutting tools can also be improved by ion implantation. For a general discussion of the techniques and potential advantages of ion implantation, see generally S. Picraux, et al., "Ion Implantation of Surfaces", Scientific American, Vol. 252, No. 3, pp. 102-113, 1985; D. M. Hulett, et al., "Ion Nitriding and Ion Implantation: A Comparison," Metal Progress, August 1985, pp. 18-21; V. M. Cassidy, "Ion Implantation Process Toughens Metalworking Tools," Modern Metals, September 1984, pp. 65-67.
While commercially viable applications of conventional ion implantation techniques have been demonstrated, the relatively high cost of the process has limited its use thus far to high unit cost items having very special applications. A significant factor in the substantial production costs of conventional ion implantation is that significant and time-consuming manipulation of the ion beam and the target is required to obtain implantation over the entire surface of a three-dimensional target. In conventional ion implantation, the ions are extracted from a plasma source and focused into a beam which is accelerated to the desired energy and then rastered across one face of the target to uniformly implant the surface of that face. Because of the line of sight nature of this ion implantation technique, a manipulator platform or stage is required which can support the target for rotation in the beam so that all sides of the target can be implanted. The need to manipulate a three-dimensional target to allow all sides of the target to be implanted adds cost and complexity, constrains the maximum size of the target which can be implanted, and increases the total time required to obtain satisfactory implantation of all target surfaces for relatively large targets. Because the ions travel to the target in a largely unidirectional beam, it is often necessary to mask targets having convex surfaces so that ions are allowed to strike the target only at angles substantially normal to the target surface. Normal incidence of ions to the surface is preferred since as the difference in the angle of incidence from the normal increases, sputtering increases and the net retained dose in the target decreases.